In combustion furnaces which burn, at high temperatures, solid hydrocarbon fuel obtained through pyrolysis of coal, coke, biomass, industrial wastes, and the like, and in gasification furnaces which gasify the solid hydrocarbon fuel, the temperature in the furnace needs to be controlled at an optimum temperature based on a measurement value of the in-furnace temperature, in order to appropriately advance the reaction in the furnace. The optimum temperature is about 1300 to 1600° C., which is a very high temperature.
Further, in combustion furnaces and gasification furnaces of this type, highly corrosive gas or molten ash of solid fuel is generated.
In particular, in coal gasification furnaces, the in-furnace temperature becomes about 1600° C., which is a high temperature that would not be seen in conventional industrial facilities, and in addition, the in-furnace pressure becomes about 2.5 MPa, which is a very high pressure. Further, slag containing a large amount of reductive carbon is present in the furnace, and this causes highly corrosive gas atmosphere in the furnace, in conjunction with the high temperature environment.
Therefore, combustion furnaces and gasification furnaces in which gas is generated need hermetical-type in-furnace temperature measurement devices that can measure the in-furnace temperature without leaking atmospheric gas in the furnace.
Conventionally, such a hermetical-type in-furnace temperature measurement device includes a support tube connected to a measurement hole which leads to the inside of the furnace, and a sensor protection tube which includes therein a temperature sensor composed of a thermocouple. In the hermetical-type in-furnace temperature measurement device, the protection tube is hermetically housed in the support tube such that a leading-end portion of the sensor protection tube corresponding to a temperature-sensing portion of the temperature sensor is always exposed in the furnace (for example, see Patent Literature 1 and 2).